Z87 Haswell build suggestion

1. overclocking

there is absolutely no harm in overclocking as long as you stay within the bounds of that CPU. If they pushed every CPU to its limits then the difference between there top chips and the middle would not have enough disparity to make people want to spend more. I would have to dig for the old articles that i have read that show how overclock does not need to be tuned down overtime. In other words when a CPU is pushed to hard overtime you would have to lower clocks as things started to break down. the intel chips have not shown this propensity and as long as your cooling solution is adequate then you are safe. The asus built in utilities do a very good job of overclocking and doing it safely, if it did not then 1000's of customers would be crying about how asus software blew up there computer and you just do not find this.
hell toms recommends the k edition chips and the only reason to buy a k edition chip is to overclock.

2. bang for your buck and hyper threading

bang for your buck is all dependent on what you are doing.
http://software.intel.com/en-us/articles/intel-hyper-threading-technology-your-questions-answered
intel q/a above and it seems at best you can get another 20% performance if you running something that is max out all four CPU cores. there are not to many instances where this will occur. So what you gain over an i5 is not that significant unless you are running a business that uses the software that needs that much power and this would lead to a cost savings as employees get more done per hour.

3. which motherboard

well they all seem to support at least 2133 MHz ram which is plenty fast enough. It really comes down to which features are you willing to pay for. the rog and other premium boards come with the overclocking software some asus motherboards are not supported. that software is worth every penny if you want to safely overclock your computer including the ram. and while rog does stand for republic of gamers it is really just geared towards enthusiasts and most gamers fall into this realm.
http://dlcdnet.asus.com/pub/ASUS/mb/LGA1150/SABERTOOTH-Z87/SABERTOOTH-Z87_DRAM_QVL.pdf

the rog board does have a high quality audio controller that you can tweak wattage in the bios. not sure if audio quality is a concern.

in the end any of the asus boards will work and as long as you get the software and features i would buy whatever fits your needs. most things are standardized in each platform as far a z 78 and such goes